The effective multiplicity of infection for HCMV depends on activity of the cellular 20S proteasome.

Human cytomegalovirus (HCMV) is a betaherpesvirus capable of infecting numerous cell types and persisting throughout an infected individual's life. Disease usually occurs in individuals with compromised or underdeveloped immune systems. Several antivirals exist but have limitations relating to toxicity and resistance. HCMV replication involves upregulation of host proteasomal activities which play important roles in the temporal stages of replication. Here, we defined the impact on replication kinetics of the proteasome inhibitor, bortezomib. We demonstrate that bortezomib significantly reduces levels of viral genomes and infectious virions produced from a population of cells. Inhibition reduced expression of viral proteins that are influenced by genome synthesis. When added prior to 24 hpi, we observe decreases in PCNA and Cdk1 while increases in p21 whose regulations contribute to efficient replication. This response synergized with an antiviral, maribavir. Since some replication occurred, we tested the hypothesis that a subset of infected cells might break through inhibition. Initially, we simulated bortezomib activities using a mechanistic computational model of late-lytic replication. Upon reducing MOI IMPORTANCE: HCMV infection and reactivation continues to contribute to morbidity and mortality around the world. Antiviral compounds are available but have limitations. Here, we have defined the impact of the proteasome inhibitor bortezomib on HCMV replication. Proteasomal activities play a critical role in temporal changes required for replication. We demonstrate that disrupting these activities inhibits viral replication while likely supporting increased antiviral activity of the anti-HCMV agent, maribavir. Using a combination of live cell imaging and computational tools, we discover that a subset of infected cells progresses to fulminant infection which we define as the effective MOI, and this subset would otherwise be missed when analyzing the average of the population.